We demonstrate an alternative concept of laser wavelength conversion to the NIR – SWIR range with simultaneous multiple spectral broadening based on transient stimulated Raman chirped pulse amplification (TSRCPA) and pulse compression to fs pulsewidth for the sub-TW class lasers, with possible application in the next generation LIDARs. Transform limited pulses of a Yb:YAG laser with a duration of ~1.2 ps were used to pump a multistage TSRCPA based on KGW crystals seeded with 1100 – 2500 nm supercontinuum. A 16-times spectral broadening was shown after TSRCPA compared to pump pulses, conversion efficiency 55%, and compression to ~145 fs. This concept, extended for gases and diamond with larger Stokes shifts, allows further exploration of SWIR range, especially for the 2nd Stokes.
The ability to identify explosives by ultrasonic spectra up to 45 kHz has been investigated for forensic and anti-terror applications. To lower the threshold for laser initiation, nontrivial and well-known azides, CTAP, HMDT, ETN, HMX and other energetic materials have been synthesized. Upon initiation of copper azide by Nd:YAG laser with 11 ns pulsewidth, a threshold of only ~80 μJ was reached, and for 50 μs pulses of laser diode it was ~300 μJ, which is consistent with the thermal initiation nature. Significant differences were found in the spectrum of high-frequency acoustic and ultrasonic vibrations for various energetic materials and bilayer structures. The effective frequency range for the dissociation of copper azide, silver azide and HMTD is limited by ~27 kHz. The spectra of bilayer structures demonstrate suppression of the characteristic lines of copper azide and enrich the spectrum in the ~27 – 45 kHz range: ETN appears in relatively wide bands, while HMX modulates the spectrum with periodic ~3 kHz bands. If successful, the discovered patterns can be used in disaster forensics.
In this study, we present the results of copper azide Cu(N3)2 initiation by pulsed lasers. The threshold energy and energy density are defined. A comparison of the obtained results shows the similarity of initiation of silver azide and copper azide. An approach to improving the safety of the use of cooper azide is proposed.
We report results of design and optimization of high average power picosecond and nanosecond laser operating at 1342 nm wavelength. This laser is comprised of master oscillator, regenerative amplifier and output pulse control module. Passively mode-locked Nd:YVO4 master oscillator emits ~ 10 ps pulses at repetition rate of 55 MHz with average output power of ~ 100 mW. These pulses were used to seed regenerative amplifier based on composite diffusion-bonded Nd:YVO4 rod with variable Nd doping concentration pumped at 880 nm wavelength. Laser produces 10.9 ps pulses at 300 kHz repetition rate with average output power of 11 W and nearly diffraction limited beam quality M2 ~ 1.03. Fraction of laser output was converted to the second harmonics with 60 % efficiency providing the average power of 5 W at 671 nm wavelength. Without seeding the regenerative amplifier transforms to electro-optically cavitydumped Q-switched laser delivering 10 ns pulses at high repetition rates with beam propagation factor of M2 ~ 1.06.
We demonstrate results of design and optimization of high average output power picosecond laser operating at 1342 nm wavelength for selective material processing. This laser is comprised of mode locked master oscillator, regenerative amplifier and output pulse control module. Passively mode locked by means of semiconductor saturable absorber and pumped with 808 nm wavelength Nd:YVO4 master oscillator emits pulses of ~ 13 ps duration at repetition rate of 55 MHz with average output power of ~ 140 mW. The four-pass confocal delay line with image relay forms a longest part of the oscillator cavity in order to suppress thermo-mechanical misalignment. Optimization of the intracavity pulse fluence ensures significant lifetime improvement for the saturable absorber. This oscillator was used as the seeder for regenerative amplifier based on composite diffusion-bonded Nd:YVO4 rod pumped with 880 nm wavelength. When operating at 300 kHz repetition rate the laser delivers high quality output beam of M2 ~ 1.1 with average power in excess of 10 W at 1342 nm wavelength.
We present results of beam quality investigation in Nd:YAG crystal fiber amplifier seeded by ns, sub-ns and ps laser
pulses counter-propagating to continuous pump of < 110 W power at 808 nm wavelength. The maximum amplified
power of 44 W and energy of 3.2 mJ has been achieved with ns seed. We observed gain rise to < 75 with ps seed of
1.6 mW average power when tuned emission spectra to ~ 1064.3 nm. Beam propagation coefficient M2 approach 1.2 at
the maximum pump power with high quality seed pulse emitted by 6 ps fiber laser. Amplification of sub-ns seed pulses
from microchip laser led to an M2 increase from ~1.2 to ~< 1.5. New analytical solution for temperature distribution in
end-pumped thin long single crystal fiber with temperature dependent thermal conductivity coefficient is found for
polynomial transverse pump distribution. The analytical relation between thermal coefficients of refractive index at zero
stresses and zero strains is found for YAG type cubic crystals. Using plane strain approximation the analytical expression
for thermal radial and tangential changes of refractive index is found, and the relation between different expressions for
so-called photoelastic constants Cr,θ is established. The methods of numerical calculation of rays and Gaussian beam
propagation in a graded-index medium of active element are developed. The error in widely used formula for M2 of
Gaussian beam with quartic phase aberration is corrected. It is shown that beam quality degradation can be explained by
active thermal lens in power amplifier when changes of transverse beam shape or beam width during amplification are
taken into account.
We demonstrate 220 W average power at 355 nm from a diode-pumped acousto-optically Q-switched Nd:YAG laser using intracavity second harmonic generation and sum frequency mixing in a nested sub-cavity design. The laser generates linearly polarised pulses with duration 65 ns at repetition rate 10 kHz. Polarisation multiplexing is used to combine two orthogonal beams giving total output pulse energy 22 mJ with peak power <0.3 MW in an unpolarised multimode beam with smooth gaussian-like transverse intensity distribution. The combination of high peak power and high average power in a multimode beam enables the use of low maintenance, low cost of ownership DPSS lasers for high-throughput industrial processes in the UV.
We demonstrate power scaling of an Nd:YAG picosecond master oscillator power amplifier system to over 200 W. The ‘z-slab’ amplifier design is a power scalable, edge-pumped zigzag slab amplifier architecture, and it is demonstrated here in two alternative multi-stage implementations at 1064 nm using a picosecond seed laser. In a simple design, an average power of 225 W was generated with up to 450 μJ pulse energy at 11 ps pulse duration. In a compact multi-pass design, 150 W was generated with M2 < 1.75.